Performance of Procalcitonin to Distinguish Fungal from Bacterial Infections in Patients with Systemic Lupus Erythematosus

Purpose: To evaluate the performance of serum procalcitonin (PCT) concentrations to diagnose fungal infection in patients with systemic lupus erythematosus (SLE). Patients and Methods: From January 2017 to October 2020, SLE patients hospitalized for serious infection with an identified single bacterial or fungal pathogen, as well as PCT measured within 24h after admission were included. The diagnostic performance of PCT was evaluated independently and in combination with the white blood cell (WBC) count, C-reactive protein (CRP) level, and erythrocyte sedimentation rate (ESR). The analysis included the sensitivity, specificity, positive and negative predictive values, positive and negative likelihood ratios, and the crude and adjusted area under the receiver operating characteristic curve (AUROC). Results: Sixty-nine patients were included; 26 had a fungal infection (38%) and 43 had a bacterial infection (22 gram-positive and 21 gram-negative). Fungal infection patients were mainly distributed in the respiratory group (88.5%), and bacterial infection distribution were more prevalent in respiratory group (44.2%) and abdominal/urinary group (23.3%). The PCT concentration was significantly lower in fungal infections than bacterial infections (fungal: 0.22 ng/mL, interquartile range [IQR], 0.09-0.44 vs bacterial: 0.60 ng/mL, IQR, 0.16-5.74; p = 0.016) and differed significantly between different infection sites (p = 0.022). PCT had better diagnostic performance for predicting fungal infection (AUROC = 0.731) than the WBC count (AUROC = 0.581), the CRP level (AUROC = 0.716), and ESR (AUROC = 0.583). PCT and ESR together had the best diagnostic performance, with 46.2% sensitivity and 88.4% specificity. Further, the AUROC increased compared to PCT alone but was statistically insignificant (p = 0.693). Conclusion: For SLE patients with serious infection, the PCT concentration had better diagnostic accuracy for predicting fungal infection than the WBC count, the CRP level, and ESR. Combining PCT and ESR obtained the highest AUROC and provided an acceptable discrimination performance.